In the disclosure of the present invention reference is mostly made to the treatment of diabetes by injection or infusion of insulin, however, this is only an exemplary use of the present invention.
Portable drug delivery devices for delivering a drug to a patient are well known and generally comprise a reservoir adapted to contain a liquid drug and having an outlet in fluid communication with a transcutaneous access device such as a hollow infusion needle or a cannula, as well as expelling means for expelling a drug out of the reservoir and through the skin of the subject via the access device. Such drug delivery devices are often termed infusion pumps.
Basically, infusion pumps can be divided into two classes. The first class comprises infusion pumps which are relatively expensive pumps intended for 3-4 years use, for which reason the initial cost for such a pump often is a barrier to this type of therapy. Although more complex than traditional syringes and pens, the pump offer the advantages of continuous infusion of insulin, precision in dosing and optionally programmable delivery profiles and user actuated bolus infusions in connections with meals.
Addressing the above problem, several attempts have been made to provide a second class of drug infusion devices that are low in cost and convenient to use. Some of these devices are intended to be partially or entirely disposable and may provide many of the advantages associated with an infusion pump without the attendant cost and inconveniencies, e.g. the pump may be prefilled thus avoiding the need for filling or refilling a drug reservoir. Examples of this type of infusion devices are known from U.S. Pat. Nos. 4,340,048 and 4,552,561 (based on osmotic pumps), U.S. Pat. No. 5,858,001 (based on a piston pump), U.S. Pat. No. 6,280,148 (based on a membrane pump), U.S. Pat. No. 5,957,895 (based on a flow restrictor pump (also known as a bleeding hole pump)), U.S. Pat. No. 5,527,288 (based on a gas generating pump), or U.S. Pat. No. 5,814,020 (based on a swellable gel) which all in the last decades have been proposed for use in inexpensive, primarily disposable drug infusion devices, the cited documents being incorporated by reference.
As the membrane pump can be used as a metering pump (i.e. each actuation (or stroke) of the pump results in movement of a specific amount of fluid being pumped from the pump inlet to the pump outlet side) a small membrane pump would be suitable for providing both a basal drug flow rate (i.e. providing a stroke at predetermined intervals) as well as a drug bolus infusion (i.e. a given number of strokes) in a drug delivery device of the above-described type.
More specifically, a metering membrane pump may function as follows. In an initial condition the pump membrane is located at an initial predefined position and the inlet and outlet valves are in their closed position. When the means for moving the membrane (i.e. the membrane actuator) is energized an increase of the pressure inside the pumping chamber occurs, which causes opening of the outlet valve. The fluid contained in the pumping chamber is then expelled through the outflow channel by the displacement of the pump membrane from its initial position towards a fully actuated position corresponding to the end position for the “out-stroke” or “expelling-stroke”. During this phase, the inlet valve is maintained closed by the pressure prevailing in the pumping chamber. When the pump membrane is returned to its initial position (either due to its elastic properties or by means of the membrane actuator) the pressure in the pumping chamber decreases. This causes closing of the outlet valve and opening of the inlet valve. The fluid is then sucked into the pumping chamber through the inflow channel, owing to the displacement of the pump membrane from the actuated position to the initial position corresponding to the end position for the “in-stroke” or “suction-stroke”. As normally passive valves are used, the actual design of the valve will determine the sensitivity to external conditions (e.g. back pressure) as well as the opening and closing characteristics thereof, typically resulting in a compromise between the desire to have a low opening pressure and a minimum of backflow. As also appears, a metering membrane functions as any conventional type of membrane pump, for example described for use as a fuel pump in U.S. Pat. No. 2,980,032.
As follows from the above, the precision of a metering pump is to a large degree determined by the pump membranes movement between its initial and actuated positions. These positions may be determined by the pump cavity in which the pump membrane is arranged, i.e. the membrane is moved between contact with two opposed surfaces, this allowing e.g. the pump to be driven by an expanding gas (see PCT/DK03/00628), or they may be determined by a membrane actuator member being moved between predefined positions. Indeed, to secure a high delivery precision it would be desirable to monitor that the pump membrane is actually moved between its two positions. Membrane movement may be measured using any convenient means such as electrical contacts or electrical impedance measurement (resistance or capacitance) between electrical contacts/elements arranged on opposed surfaces of the pump membrane and the pump housing.
Instead of, or in addition to, monitoring the pump per se it is also possible to positively detect the flow rate from any given type of pump by incorporating additional metering means, e.g. based on thermo-dilution as disclosed in EP 1 177 802.
To further monitor proper functioning of an actuated system such as a drug infusion pump, it would be desirable to provide means for detecting different operational conditions of the system, such as an occlusion condition downstream of a pump, e.g. full or partial occlusion of a transcutaneous access device. As the outlet conduit leading from the pump outlet to the distal outlet opening of a transcutaneous access device is relatively stiff, a given pressure rise in the outlet conduit during pump actuation can normally be taken as an indication for an occlusion condition and thus be utilized to detect the latter. For example, US 2003/167035 discloses a delivery device comprising pressure sensors being actuated by a resilient diaphragm arranged in flow communication with in the outlet conduit.
Having regard to the above-identified problems, it is an object of the present invention to provide an actuator system, or component thereof, suitable for driving an actuatable structure or component.
It is a further object to provide an actuator system which allows for detection of different operational conditions of the system, thereby ideally providing a system which can be actuated and controlled in a safe and efficient manner.
It is a further object to provide an actuator system which can be used in combination with a pump assembly arranged in a portable drug delivery device, system or a component therefore, thereby providing controlled infusion of a drug to a subject.
It is a further object to provide an actuator system which can be used in combination with a pump such as a membrane pump.
It is a further object of the invention to provide an actuator, or component thereof, which can be provided and applied in a cost-effective manner.